Abstract: A method and corresponding apparatus for ranging an Optical Network Terminal (ONT) in a Passive Optical Network (PON) is provided. An example method may include: (i) transmitting a ranging request from an Optical Line Terminal (OLT) to an ONT in connection with a transport layer ranging window; (ii) monitoring for a ranging response from the ONT during at least one physical layer ranging window within the transport layer ranging window, the transport layer ranging window having a duration longer than the physical layer ranging window; and (iii) determining at least one metric associated with the ranging response for use in connection with upstream communications between the ONT and the OLT. The metric(s), used in connection with upstream communications, are accurately determined, and communications faults during normal operations are thus reduced.